public interface IStackWalk {
// Public Instance Methods
public void Assert( );
public void Demand( );
public void Deny( );
public void PermitOnly( );
}
Permission classes that use stack walks to resolve security demands
implement the IStackWalk interface. These include
the PermissionSet class, as well as the
CodeAccessPermission class, from which all
standard code-access and identity permissions inherit.
IStackWalk defines the Demand(
) method, which duplicates the method of the same name
defined in the IPermission interface. However, the
IStackWalk.Demand( ) method initiates a
stack-walk-based security demand, whereas
IPermission.Demand( ) is not intended to use the
call stack to resolve security demands. The Assert(
), Deny( ), and PermitOnly(
) methods annotate the call stack frame of the code from
which they are executed, and affect the stack walk process initiated
by a Demand( ) call.
Assert( ) allows code to vouch for the permissions
of the callers above it on the call stack. During a stack walk, if a
demanded permission matches, or is a subset of, the asserted
permission, the stack walk terminates successfully without evaluating
further stack frames. If the asserted permissions provide only a
partial match of those demanded, the stack walk continues but only
for the remaining unasserted permissions. Code must have been granted
a permission in order to assert it, and the code must have the
permission to assert defined by the
System.Security.Permissions.SecurityPermission
class.
Deny( ) has the opposite effect of
Assert( ). If the demanded permission matches, or
is a subset of the denied permission, the stack walk is terminated,
and the runtime throws a SecurityException to the
code that initiated the Demand( ).
PermitOnly( ) functions as an inverted
Deny( ). Instead of specifying the permissions
that should terminate a stack walk, PermitOnly( )
specifies those permissions that permit the stack walk to continue
unaffected. PermitOnly( ) provides a more concise
way of denying large sets of permissions without the need to specify
them all in a Deny( ) override.
